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Development and testing of a self administered version of the Freezing of GaitQuestionnaire

Nilsson, Maria H; Hariz, Gun-Marie; Wictorin, Klas; Miller, Michael; Forsgren, Lars; Hagell,PeterPublished in:BMC Neurology

DOI:10.1186/1471-2377-10-85

2010

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Citation for published version (APA):Nilsson, M. H., Hariz, G-M., Wictorin, K., Miller, M., Forsgren, L., & Hagell, P. (2010). Development and testingof a self administered version of the Freezing of Gait Questionnaire. BMC Neurology, 10, [85].https://doi.org/10.1186/1471-2377-10-85

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RESEARCH ARTICLE Open Access

Development and testing of a self administeredversion of the Freezing of Gait QuestionnaireMaria H Nilsson1,2*, Gun-Marie Hariz3,4, Klas Wictorin5, Michael Miller1, Lars Forsgren4, Peter Hagell1

Abstract

Background: The Freezing of Gait Questionnaire (FOGQ) was developed in response to the difficulties of observingand quantifying freezing of gait (FOG) clinically as well as in laboratory settings. However, as the FOGQ is aclinician-administered patient-reported rating scale it cannot be used in postal surveys. Here we report thedevelopment and measurement properties of a self-administered version of the FOGQ (FOGQsa).

Methods: A clinical sample and a postal survey sample of non-demented people with Parkinson’s disease (PD;total n = 225) completed the FOGQsa and questionnaires concerning physical functioning (PF) and fall-related selfefficacy (FES). Additional questions (No/Yes) regarded previous falls and whether they were afraid of falling. Theclinical sample was also assessed with the Unified PD Rating Scale (UPDRS). Thirty-five participants completedFOGQsa and were also assessed with the original version (FOGQ) in a clinical interview.

Results: There were no differences (P = 0.12) between FOGQ (median, 10; q1-q3, 2-14) and FOGQsa (median, 8; 2-14) scores. The Spearman (rs) and intra-class correlations between the two were 0.92 and 0.91 (95% CI, 0.82-0.95),respectively. For FOGQsa, corrected item-total correlations ranged between 0.68-0.89. Reliability was 0.93 (95% CI,0.91-0.94). FOGQsa scores correlated strongest with UPDRS Item 14 (Freezing; rs, 0.76) and with FES (rs, -0.74). Theweakest correlation was found with age (rs, 0.14). Fallers scored significantly (p < 0.001) higher on FOGQsacompared to non-fallers, median scores 8 (q1-q3, 4-14) versus 2 (0-7). Those expressing a fear of falling scoredhigher (p < 0.001) than those who did not, median scores 2 (0-7) versus 6 (2-14).

Conclusions: The present findings indicate that the FOGQsa is as reliable and valid as the original interviewadministered FOGQ version. This has important clinical implications when investigating FOG in large scale studies.

BackgroundUp to 50% of people with Parkinson’s disease (PD)experience sudden and transient motor blocks (freezing)while initiating or performing activities [1]. Freezing ofgait (FOG) is often described as if the feet are glued tothe ground [1,2]. This description is recommended touse when asking people with PD about the phenomenon[3]. FOG typically appears when initiating the first step(start hesitation), on turning or when approaching a tar-get (destination hesitation or “target freezing”) [1,2].FOG is usually evoked in crowded and confined spacesas well as in time limiting situations, e.g., when crossinga street [1,2,4-7].The presence and severity of FOG has been found to

be associated with longer disease duration [1,7,8], more

advanced disease stage [1,7,8], falls [6,9-13], dyskinesias[1] and decreased mobility [14]. FOG is in fact one ofthe most distressing symptoms in PD [15], and it has anegative impact on patient perceived health [14,16].FOG is characterized by its unpredictable and episodic

nature. It typically occurs as short lasting episodes athome, which makes it difficult to observe and quantifyduring clinical testing as well as in laboratory settings[17,18]. Evaluating FOG is commonly done by eitherposing a question or by using a single item assessmentsuch as item 14 of the Unified PD Rating Scale(UPDRS) [8-10,13]. Therefore, Giladi et al. developedthe Freezing of Gait Questionnaire (FOGQ) which is aclinician/interview administered patient-reported ratingscale [19]. The FOGQ consists of six items scored from0-4. The total score ranges from 0 to 24, and higherscores denote more severe FOG.* Correspondence: Maria_H.Nilsson@med.lu.se

1Department of Health Sciences, Lund University, Lund, SwedenFull list of author information is available at the end of the article

Nilsson et al. BMC Neurology 2010, 10:85http://www.biomedcentral.com/1471-2377/10/85

© 2010 Nilsson et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative CommonsAttribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction inany medium, provided the original work is properly cited.

The FOGQ was originally tested for reliability (Cron-bach’s alpha, 0.94) and validity in 40 people with PD[19]. However, although the FOGQ appears to be a use-ful and valid tool for its purpose, the dependency on aclinician to interview the patient and to demonstrate themeaning of FOG is also limiting. For example, the toolbecomes somewhat time consuming for implementationin clinical practice and cannot be used for larger scalepostal surveys. A completely self-administered FOGQscale that provides the same type of information wouldtherefore be of great benefit.This study assessed the validity and reliability of a self-

administered version of the FOGQ, i.e. the FOGQsa. Inaddition, we explored the relationships betweenFOGQsa scores and patient demographics, fear of fall-ing, falls, gait, motor complications and physicalfunctioning.

MethodsThe study was divided into two phases: (1) developmentof a self-administered version of FOGQ (the FOGQsa)and (2) testing the psychometric properties of theFOGQsa.

Development of the FOGQsaThe intention was to preserve the semantic content ofall six original FOGQ items but with revisions of thewording to make them applicable for self-administra-tion. In accordance with the original FOGQ instrument[19], responses should be based on experiences over thelast week except for item 3. As in the original FOGQscale, all items are scored from 0-4 (possible total scorerange, 0-24; higher scores = more severe FOG).To substitute for the demonstration and description of

FOG in the FOGQ, a cover sheet explaining the FOGphenomenon was developed for the FOGQsa. Thedescription was based on a review of the literature, andit was constructed in close interaction with two nursesand two neurologists specialized in PD. The cover sheetdescribes that FOG is typically experienced as if “thefeet are glued to the ground”, and that this can happenwhile trying to initiate walking, while walking (whichcould be accompanied by taking smaller and smallersteps) or while turning. Other provocative factors arealso described such as walking in confined spaces (e.g.passing a doorway), target hesitation (e.g. just beforeapproaching a chair when sitting down) and when hav-ing limited time (e.g. crossing a street) [1,2,4-7].Following modification of the FOGQ into the

FOGQsa, face-to-face field-test interviews were con-ducted with 14 non-demented people with PD (9 men)with varying degrees of motor complications and/or gaitdisturbances to assess clarity of wording, face validityand respondent burden.

Psychometric properties of the FOGQsaParticipantsData collection included a clinical sample and a postalsurvey sample of non-demented people with idiopathicPD [20].The clinical sample consisted of a convenience sample

with varying degrees of motor complications and/or gaitdisturbances receiving out-patient care at a Swedish uni-versity hospital (Table 1). Fifty patients were invited toparticipate. Eight patients declined participation and fivepatients were unable to attend the study appointment.An additional participant did not complete the FOGQsaand was therefore excluded. Thus, 36 participants wereincluded.The postal survey sample was recruited from another

Swedish university hospital (Table 1). The survey wassent to 282 patients (39% female), and 231 werereturned, of which 191 were completed (43% female;conservative total response rate, 68%). Thirty-eight ques-tionnaires were returned completely blank and two werereturned to sender due to change of address. Out of the191 responders, two had left all items of the FOGQsablank. These two participants were excluded, leaving189 participants for analyses. Demographic data of all225 participants are presented in Table 1.InstrumentsAll participants completed the FOGQsa, the Swedishversion of the Falls-Efficacy Scale, FES(S) [21], and thePhysical Functioning (PF) scale of the Medical Out-comes Study 36-Item Short-Form Health Survey (SF-36)[22].FES(S) assesses fall-related self-efficacy, and the 13

activities are rated from 0 (not confident at all) to 10(completely confident) [21]. The total score can rangefrom 0 to 130. PF comprises ten items about physicalactivities [22]. The score can range from 0 to 100,where higher scores denote better physical functioning.Additional questions included whether participants hadfallen during the past six months (No/Yes) and if theywere afraid of falling (No/Yes). The clinical sample wasalso asked whether they felt unsteady while turning(No/Yes).ProcedureThe FOGQsa was mailed to the clinical sample beforethe study visit. The participants were instructed to com-plete it three days before the visit, put the completedquestionnaire in an envelope, seal it and bring it to thestudy visit. Demographic data (Table 1) were collectedthrough self report for all participants, which the clinicalsample completed at their out-patient visit. Demographicquestions preceded the included self-administered ques-tionnaires. In addition, the clinical sample was assessedwith timed gait tests: ten meter walk test (gait speed,both comfortable and fast) and Timed Up & Go (TUG).

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Each gait test had one practice trial and one test trial.The FOGQ was thereafter administered as a clinicalinterview including a demonstration of FOG [19]. Thatis, the assessor demonstrated typical manifestations ofstart hesitation, freezing at the doorway and while turn-ing. Finally, clinical assessments according to the UPDRSand Hoehn & Yahr stages (HY) [23] were conducted byan independent assessor who was unaware of previoustest results. HY was also assessed for the “off” phasebased on patient-reported history. In the postal surveysample, self administered versions of UPDRS items 13(falling), 14 (freezing) and 15 (walking) were included[24]. All participants of the postal survey sample receiveda reminder about ten days after the first administration.

The study was reviewed by the local ethics advisorycommittee, and the included participants gave theirwritten informed consent.Analyses The primary aim of the analyses was toexplore to what extent the FOGQsa scores reproducedthe findings of the original FOGQ instrument [7,19,25].We thus explored whether the assumptions for sum-

ming FOGQsa item scores into a total score were met[26]. That is, we examined whether item mean scoresand standard deviations were roughly similar and if thecorrected item-total correlations exceeded 0.3. Whetherthe items appear to represent a common variable wasconsidered supported if corrected item-total correlationswere ≥0.4 [26].

Table 1 Participants’ characteristics

Total samplen = 225

Clinical samplen = 36

Postal surveyn = 189

Mean age, years (SD, min.-max.) 69.1 (8.9) 65.3 (6.2) 69.9 (9.1)

42.0-91.0 49.0-83.0 42.0-91.0

n = 221 n = 36 n = 185

Mean PD-duration, years (SD, min.-max.) 7.7 (6.8) 14.6 (8.3) 6.2 (5.5)

0.33-44.0 2.2-44.0 0.33-28.0

n = 210 n = 36 n = 174

Gender (men/women), n (%) 137 (62%)/ 29 (81%)/ 108 (58%)/

84 (38%) 7 (19%) 77 (42%)

n = 221 n = 36 n= 185

Falls past 6 months (yes/no), n (%) 88 (40%)/ 19 (53%)/ 69 (38%)/

131 (60%) 17 (47%) 114 (62%)

n = 219 n = 36 n = 183

Fear of falling (yes/no), n (%) 94 (43%)/ 9 (25%)/ 85 (46%)/

125 (57%) 27 (75%) 98 (54%)

n = 219 n = 36 n = 183

Median, q1-q3 Median, q1-q3 Median, q1-q3

Falls-Efficacy Scale (S) 112.0 106.5 114.0

75.0-130.0 94.8-129.0 69.0-130.0

n = 183 n = 30 n = 153

Physical Functioning (PF, SF-36) 55.0 24.0 60.0

29.0-75.0 20.0-28.0 35.0-80.0

n = 218 n = 30 n = 188

Item 13, UPDRS II (Falling) 0.0 0.0 0.0

0.0-1.0 0.0-1.0 0.0-1.0

n = 223 n = 36 n = 187

Item 14, UPDRS II (Freezing) 0.0 0.0 0.0

0.0-1.0 0.0-1.8 0.0-1.0

n = 221 n = 36 n = 185

Item 15, UPDRS II (Walking) 1.0 1.0 1.0

0.0-2.0 0.0-1.0 0.0-2.0

n = 221 n = 34 n = 187

Falls-Efficacy Scale, Swedish version; the total score can range between 0-130 (higher scores = better).

Physical Functioning (PF, SF-36); total score range between 0-100 (higher scores = better).

Item 13, 14 and 15 of the UPDRS part II; each item graded from 0-4 (higher scores = greater severity).

Additional data regarding the participants are presented in Table 3.

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Floor and ceiling effects (i.e., the proportion of peopleobtaining minimum and maximum scores, respectively)were examined, and should be <15-20% [27,28]. Reliabil-ity (Cronbach’s alpha) was also estimated, and should be≥0.8 [29]. In addition, the standard error of measure-ment (SEM) was estimated using the formula:

SEM SD 1 = × −√( )

Using data from the clinical sample, we assessed therelationship between the original FOGQ and theFOGQsa through Spearman (rS) and intra-class correla-tions (ICC; one-way random model). The correlationswere expected to be strong (>0.8) in order to supportcriterion-related validity. Construct validity was assessedby examining the pattern of correlations (rS) betweenFOGQsa and UPDRS scores. To replicate the patternsreported for the original version of FOGQ [19,25], thecorrelation with FOGQsa scores was expected to bestrongest for UPDRS part II (Activities of Daily Living,ADL) and weakest for UPDRS part I (mentation, beha-vior and mood) [7,19,25]. Among individual UPDRSitems, we expected a stronger correlation betweenFOGQsa scores and item 14 (freezing) than with items13 (falling unrelated to freezing), 15 (walking), 29 (gait)and 30 (postural stability) [19,25]. The correlation withdisease severity (HY) was expected to be stronger in the“off” state than in the “on” state [25].In addition, we examined the relationships between

FOGQsa scores and patient demographics, FES(S),timed gait tests, dyskinesias (items 32-35 of the UPDRSpart IV), motor fluctuations (items 36-39 of the UPDRSpart IV) and PF. We expected the FOGQsa scores tocorrelate stronger with dyskinesia, motor fluctuationsand FES(S) scores than with gait tests [25]. The weakestcorrelation was expected with age [25]. We also assesseddifferences (Mann-Whitney U test) in FOGQsa scoresbetween people who did and did not report falls, fear offalling and unsteadiness while turning. It was expectedthat fallers, those reporting fear of falling and thosebeing unsteady while turning would score higher.Analyses were performed using SPSS 15 (SPSS Inc.,

Chicago, IL) and ScoreRelCI (Barnette 2005). Two-tailedp-values <0.05 were considered statistically significant.P-values were not corrected for multiple testing.

ResultsField-test participants had a mean age of 64 (SD, 5.2)years and an average PD-duration of 16 (SD, 5.5) years.All 14 participants found the description of FOG to beclear and understandable and items were consideredrelevant and easy to answer. One participant commen-ted that the duration of freezing was somewhat difficultto estimate. Two comments related to the frequency of

freezing. However, no changes in the questionnaire weredeemed necessary due to these comments. The meantime for completing FOGQsa was 3 (SD, 1.3) minutes.For the total sample, mean and SD for FOGQsa items

scores ranged between 0.76-1.6 and 1.1-1.4, respectively(Table 2). Corrected item-total correlations rangedbetween 0.68-0.89. Forty-one participants (19%) scored0, and none reached the maximum score of 24. Reliabil-ity was 0.93 (95% CI, 0.91-0.94), and SEM was 1.6.Results for the two subsamples were similar (Table 2).Total FOGQsa scores could be computed for 214 (95%)out of the 225 participants.Data for both the FOGQsa and the original FOGQ

were available for 35 people in the clinical sample.There were no differences (P = 0.12) between FOGQ(median, 10; q1-q3, 2-14) and FOGQsa (median, 8; q1-q3, 2-14) scores. The Spearman and intra-class correla-tions were 0.92 and 0.91 (95% CI, 0.82-0.95), respec-tively (Figure 1). The mean number of days betweencompletions was 2.6 (SD, 0.80).The relationships between FOGQsa scores and other

variables are presented in Table 3. The FOGQsa scoresfor the total sample showed the strongest correlationwith UPDRS item 14 (Freezing; rs, 0.76) and with FES(S)(rs, -0.74). The weakest correlation was found with age(rs, 0.14). For common variables, both samples showedsimilar patterns (Table 3). However, the clinical sampleshowed a stronger correlation with UPDRS part II (rs,0.68) than with FES(S) (rs, -0.57) (Table 3).FOGQsa scores did not differ (p > 0.3) between gen-

ders. For the total sample, the median score was 4 forboth women and men (q1-q3, 1-9 and 1-11, respectively).Out of the 225 participants, 219 responded to the ques-tion whether they had fallen during the past six months.Fallers (88/219; 40%) scored significantly (p < 0.001)higher on FOGQsa compared to non-fallers, medianscores 8 (q1-q3, 4-14) versus 2 (q1-q3, 0-7). Thoseexpressing a fear of falling scored higher (p < 0.001) thanthose who did not, median scores 2 (q1-q3, 0-7) versus 6(q1-q3, 2-14). In the clinical sample, those reportingunsteadiness while turning (20/35; 57%) had significantly(p = 0.030) higher FOGQsa scores than those who didnot, median scores 11 (q1-q3, 6-16) versus 2 (0-13).

DiscussionThe present findings indicate that the FOGQsa is asreliable and valid as the original interview administeredFOGQ version. Specifically, our observations supportthe legitimacy of summing item scores into a reliabletotal score that corresponds closely to FOGQ scores. Inaddition, construct validity is supported by a correlationpattern very similar to that reported for the originalFOGQ version. This has important clinical implicationswhen investigating FOG.

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Snijders et al. highlighted that the original FOGQ doesnot include provocative circumstances of FOG [3].

When using a self-administered assessment it is crucialthat the investigated construct is well defined anddescribed. The cover sheet of the FOGQsa was createdin order to make certain that the individual recognizesand fully understands the investigated phenomenon. Ittherefore included both environmental and circumstan-tial factors that may provoke FOG; narrow space (e.g.passing a doorway) [1,2,6,7], crowded space and limitedtime, e.g. trying to cross a busy street [2,4-6]. The origi-nal FOGQ does not mention target hesitation althoughFOG is known to occur when reaching a target [1,2,4,5].This new self administered version does, however,include target hesitation when describing FOG. Fieldtesting of the FOGQsa revealed that the participantsconsidered the content to be both clear and relevant.The respondent burden was marginal as indicated by ashort completion time.FOGQsa had an internal consistency reliability above

0.90 and thus exceeded the recommendation of 0.80 [29].This finding is similar to the results for the originalFOGQ version [7,19,25]. In a separate pilot study, wehave also found its test-retest reliability to be adequate(ICC, 0.85) [30]. However, further studies investigating

Table 2 Descriptive and psychometric FOGQsa data

Total samplen = 225

Clinical samplen = 36

Postal survey samplen = 189

Item Mean (SD) Corrected Item-totalcorrelations n = 214

Mean (SD) Corrected Item-totalcorrelations n = 35

Mean (SD) Corrected Item-totalcorrelations n = 179

1 “Walking during worst state” 1.6 (1.1)2 missing

0.68 1.7 (1.2)1 missing

0.87 1.6 (1.1)1 missing

0.64

2 “Gait difficulties affectingdaily activities andindependence”

1.1 (1.1)2 missing

0.68 1.2 (1.1)1 missing

0.76 1.1 (1.2)1 missing

0.68

3 “Feet getting glued to thefloor”

1.1 (1.4) 1

3 missing0.83 1.7 (1.4) 0.82 1.0 (1.4)

2 missing0.84

4 “Duration of longest freezingepisode”

0.87 (1.3)7 missing

0.89 1.6 (1.6) 0.91 0.73 (1.1)7 missing

0.90

5 “Duration of typical starthesitation”

0.76 (1.1)6 missing

0.88 1.2 (1.4) 0.85 0.67 (1.1)6 missing

0.89

6 “Duration of typical turninghesitation”

0.76 (1.1)5 missing

0.83 1.1 (1.4) 0.78 0.68 (1.1)5 missing

0.85

Total scoren = 214

Total scoren = 35

Total scoren = 179

Mean (SD) 6.1 (6.2) 8.6 (7.2) 5.6 (5.9)

Median, q1-q3 4.0, 1.0-4.0 8.0, 2.0-14.0

4.0, 1.0-9.0

Min-max 0-22 0-22 0-22

% scoring minimum(0)/maximum (24)

19/0 17/0 20/0

Reliability, Cronbach’s alpha(95% CI)

0.93 (0.91-0.94) 0.94 (0.90-0.97) 0.93 (0.91-0.94)

FOGQsa: Freezing of Gait Questionnaire, self administered version. Each item is scored between 0-4, and the total score thus ranges between 0-24. Higher scoresdenote more severe FOG.

Some participants left certain items blank. Total scores could therefore be computed for 214 out of the 225 (95%).1 On item 3, 126 scored 0, i.e. they never experienced freezing episodes, whereas 96 out of the 214 (45%) scored at least 1 and could be defined as “freezers”.

Out of the 96 reporting freezing episodes, 51 did so “often- about once a day” and 11 “always- whenever walking”.

Figure 1 The relationship between scores of the new selfadministered version of the Freezing of gait (FOG)questionnaire (FOGQsa) and the original interviewadministered FOGQ (n = 35).

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its test-retest reliability are warranted. In the presentstudy, 19% of the participants scored 0 (best possiblescore). Both FOGQ and FOGQsa consist of six items,where four items assess FOG severity and two items con-cern gait difficulties in general. Our results thus suggestthat about 20% of the participants had neither gait diffi-culties nor FOG. In a study by Schrag et al., impaired gaitwas reported by 75% of people with a PD-duration of atleast five years [31]. In another study, 21% out of 290people with PD reported no gait problems [32]. Theobserved floor effect (i.e. percentage scoring 0) thusappears reasonable in the current targeted population.Reasonable floor and ceiling effects are a prerequisite fordetection of differences [33]. Potential differences needalso to exceed the measurement error in order to indicatea true change. The SEM observed in this study suggeststhat the change in scores need to be at least 1.7 in orderto exceed the measurement error.FOGQsa scores distinguished between fallers and non-

fallers. Both fallers and those expressing a fear of fallinghad significantly higher FOGQsa scores than those notreporting these problems. This is not surprising since

freezing is associated with falls [6,9-13]. Those whoreported being unsteady while turning also had higherFOGQsa scores than those not reporting unsteadiness. Ina study investigating 130 persons with PD, turning aroundwas the factor most commonly identified to induce freez-ing [6]. Turning is also associated with falls [9,11,34], andfalls associated with freezing are in fact more likely toresult in an injury [9]. This underlines the importance ofincluding an assessment of FOG when investigating fallsin people with PD. Availability of a self-administeredFOGQ may facilitate this in clinical practice.When assessing FOG, Snijders et al. advocate combin-

ing physical examinations with more specific questionsabout FOG [3]. However, this is not possible when con-ducting postal surveys. FOGQ scores have also beenshown to correlate only weakly with timed gait tests[25]. This indicates the need for using patient reportedtools, especially since FOG is difficult to capture duringa clinical or laboratory investigation [17,18]. The FOGQis then preferable to using a single item approach,which is less reliable and less responsive to change [35].Taken together, the present results speak in favor of

Table 3 Correlations with FOGQsa and descriptive values for clinical tests

Total samplen = 225

Clinical samplen = 36

Postal surveyn = 189

rs p-value rs p-value rs p-value

Age, years 0.14 0.046 0.07 >0.3 0.21 0.006

PD-duration, years 0.42 <0.001 0.50 0.002 0.40 <0.001

Falls-Efficacy Scale -0.74 <0.001 -0.57 0.001 -0.78 <0.001

Physical Functioning (PF, SF-36) -0.61 <0.001 -0.50 0.006 -0.68 <0.001

Item 13, UPDRS II (Falling) 0.49 <0.001 0.53 0.001 0.49 <0.001

Item 14, UPDRS II (Freezing) 0.76 <0.001 0.72 <0.001 0.78 <0.001

Item 15, UPDRS II (Walking) 0.57 <0.001 0.56 0.001 0.64 <0.001

Clinical sample, n = 36 Median (q1-q3) rs p-value

UPDRS I, Mentation, behavior and mood 2.0 (0-3.0) 0.33 0.059

UPDRS II, Activities of Daily Living 7 (3.0-13.5) 0.68 <0.001

UPDRS III, Motor examination 15.0 (8.0-20.0) 0.55 0.001

Item 29, UPDRS III (Gait) 0.5 (0-1.0) 0.46 0.006

Item 30, UPDRS III (Postural stability) 1.0 (0-2.0) 0.49 0.003

Hoehn and Yahr ("on”) 3.0 (2.0-3.0) 0.44 0.009

Hoehn and Yahr ("off”) 3.0 (3.0-4.0) 0.58 <0.001

Dyskinesias (UPDRS IV, items 32-35) 2.5 (1.0-5.0) 0.63 <0.001

Motor fluctuations (UPDRS IV, items 36-39) 3.0 (1.3-3.8) 0.60 <0.001

Timed Up & Go, sec (Mean, SD) 9.7 (2.7) 0.34 0.049

Comfortable gait speed, m/s (Mean, SD) 1.32 (0.23) -0.29 0.094

Fast gait speed, m/s (Mean, SD) 1.60 (0.40) -0.33 0.055

Falls-Efficacy Scale, Swedish version; the total score can range between 0-130 (higher scores = better).

Physical Functioning (PF, SF-36); total score can range between 0-100 (higher scores = better).

Item 13, 14 and 15 of the UPDRS part II; each item graded from 0-4 (higher scores = greater severity).

UPDRS part I; total score range 0-16 (16 = greater severity). UPDRS part II; total score range 0-52 (52 = greater severity). UPDRS part III; total score range 0-108(108 = greater severity).

Dyskinesias (UPDRS part IV, items 32-35); total score range 0-13 (13 = greater severity).

Motor fluctuations (UPDRS part IV, items 36-39); total score range 0-7 (7 = greater severity).

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using the FOGQsa when investigating FOG, falls andfear of falling in survey studies.There are some methodological concerns which need

to be taken into consideration. Demented patients wereexcluded, and the clinical sample was not randomlyselected. This might affect the external validity of thepresent findings. The lack of maximum scores may sug-gest a bias towards less severe problems in the currentsample. However, the highest observed score (22) is veryclose to the maximum score of 24, and the observedrate of people scoring zero on the FOGQsa is consistentwith observations in previous studies (see above).Furthermore, validation of the FOGQsa (as well as theFOGQ) has been based on subjective data. Future stu-dies may therefore consider adding ambulatory monitor-ing of FOG [36]. Finally, the fact that FOGQ includestwo items concerning gait difficulties in general hasbeen criticized, and these items were therefore omittedin a recent revised version of the FOGQ [37]. Therevised version supplies a video-demonstration of FOG,but it is not self-administered. We have now initiated anadaptation in order to create a self-administered versionof the revised version as well.The Swedish FOGQsa described here can be obtained

from the corresponding author. An English languageversion is under development and will also be obtainablefrom the corresponding author when available.

ConclusionsIn conclusion, we report the development and testing ofthe FOGQsa, a self administered version of the FOGQ.Its measurement properties are very similar to those pre-viously reported for the FOGQ, suggesting that it is asreliable and valid as the original interview administeredversion. Importantly, FOGQsa scores do not differ fromand correlate strongly with FOGQ scores. These findingssuggest that no substantial information is lost by usingthe self administered version as compared to the clinicianadministered FOGQ. This facilitates the investigation ofFOG in postal surveys and clinical practice. Further stu-dies are warranted in order to scrutinize the measure-ment properties of the FOGQsa in more detail.

AcknowledgementsThe authors wish to thank the patients for their cooperation; Jan Reimer,Stina Bladh, Martina Eliasson, Mona Edström and Birgitta Wikström forassistance with data collection.Funding:The study was supported by the Swedish Research Council, the SwedishParkinson Foundation, the Swedish Parkinson Academy, Skane CountyCouncil’s Research and Development Foundation, and the Faculty ofMedicine at Lund University, Lund, Sweden.This study was accomplished within the context of the Centre for Ageingand Supportive Environments (CASE), Lund University, Sweden, funded bythe Swedish Council for Working Life and Social Research.

Author details1Department of Health Sciences, Lund University, Lund, Sweden.2Department of Clinical Sciences, Division of Neurosurgery, Skåne UniversityHospital, Lund, Sweden. 3Department of Community Medicine andRehabilitation, Umeå University, Umeå, Sweden. 4Department ofPharmacology and Clinical Neuroscience, Umeå University, Umeå, Sweden.5Department of Clinical Sciences, Division of Neurology, Skåne UniversityHospital, Lund, Sweden.

Authors’ contributionsMN conceived the study (including the development of the FOGQsa),participated in its design, data collection, conducted the statistical analyses,interpreted data and drafted the first manuscript.G-M.H participated in designing the study, coordinated the survey study,participated in data collection and drafting the manuscript.KW participated in designing the study, assisted in developing the FOGQsaand drafting the manuscript.MM assisted in developing the FOGQsa and contributed to drafting themanuscriptLF participated in designing the study and drafting the manuscript.PH conceived the study (including the development of the FOGQsa),participated in its design, data collection, interpretation of data and draftingthe manuscript.All authors read and approved the final manuscript.

Competing interestsThe authors declare that they have no competing interests.

Received: 8 June 2010 Accepted: 23 September 2010Published: 23 September 2010

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doi:10.1186/1471-2377-10-85Cite this article as: Nilsson et al.: Development and testing of a selfadministered version of the Freezing of Gait Questionnaire. BMCNeurology 2010 10:85.

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